The superconducting nanowire single photon detector(SNSPD) draws much attention because of its attractive performance at ultra violet, visible, and nearinfrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material,it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles,and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with frontillumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed.Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented. The superconducting nanowire single photon detector (SNSPD) draws much attention because of its attractive performance at ultra violet, visible, and near infrared wavelengths, and it can be widespread in quantum information technologies. However, how can increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to a cavity material, it does increase when the refractive index of incident lens properties decreases; when perpendicularly polarized photons, both incident medium and cavity material play significant roles, and the absorptance curves get closer to the parallel case as the refractive index of Based on these results, two cavity-integrated SNSPDs with frontillumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed. Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.